"Sours: I'm just getting to know you a little first."
Petrus Oud Bruin
is a nice sour Flanders Red/Brown example that's not overpowering at all, and Liefmans Goudenband
is a little stronger but still easy going enough.
Verhaeghe Duchesse De Bourgogne
is another Sour Red/Brown - still more sourness balanced by a heavier sweetness (if at all I'd drink it colder to lessen the sweetness and sharpen the dry/sour qualities.)
You might find any of these at beer bars as they've been around the LCBO in pretty recent times I think... De Dolle maybe at Premier Gourmet on the right day.
Berliner Weisse and Leipziger Gose are two fairly easy-going styles that should lean to some sourness if well-made and not be overrun with sweetness like some Ontario examples. To that end I just picked up Nickel Brook Über Berliner Weisse
at Summerhill, bottle says same 3.8% ABV as NB's Green Light Berliner and I can't wait to sample its lacto sour/vinegar overtones in the flavors and aroma.
Star column Josh Rubin
Also - why be intimidated, your bottle of Gueuze Fond Tradition is just one piece of one very strange puzzle called Lambics that may take some time to fill in. And lots of risks.